First, I must commend you for not playing the blame game, and for taking ownership of having been fired and preparing to move on. While it's possible that the issue won't come up at an interview, it probably will, so you are right to anticipate the question: "Why did you leave your last job?"
The most important thing is to be honest. If you were fired, don't try to candy-coat it by saying you were laid off. (Especially since your reference will probably tell a different story.) Give a balanced account of the circumstances, and while it's fine to say that you disagree with the reasons, don't be accusatory and don't make excuses. Whether you agree or not, illustrate how you are working to improve those issues that were said to be the cause of your being fired, for example, that you are working on time management or improving your communication skills. (See also While getting fired can be a huge blow to your confidence, it's not the end of the world, so don't approach your next interview like it is.